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Polymorphisms of the vitamin D receptor gene ( VDR ) have been associated inconsistently with various diseases, across populations of diverse origin. The T(f) allele of the functional SNP  Fok I, in exon 2 of  VDR , results in a longer vitamin D receptor protein (VDR) isoform, proposed to be less active. Genetic association of  VDR  with disease is likely confounded by ethnicity and environmental factors such as plasma 25(OH)D 3  status. We hypothesized that  VDR  expression, VDR level and transactivation of target genes,  CAMP  and  CYP24A1 , depend on vitamin D, ethnicity and  Fok I genotype. Healthy volunteers participated in the study (African, n = 40 and White, n = 20). Plasma 25(OH)D 3  levels were quantified by LC-MS and monocytes cultured, with or without 1,25(OH) 2 D 3 . Gene expression and protein level was quantified using qRT-PCR and flow cytometry, respectively. Mean plasma 25(OH)D 3  status was normal and not significantly different between ethnicities. Neither 25(OH)D 3  status nor 1,25(OH) 2 D 3  supplementation significantly influenced expression or level of VDR. Africans had significantly higher mean VDR protein levels ( P <0.050), nonetheless transactivated less  CAMP  expression than Whites. Genotyping the  Fok I polymorphism by pyrosequencing together with HapMap data, showed a significantly higher ( P <0.050) frequency of the CC genotype in Africans than in Whites.  Fok I genotype, however, did not influence  VDR  expression or VDR level, but influenced overall transactivation of  CAMP  and 1,25(OH) 2 D 3 -elicited  CYP24A1  induction; the latter, interacting with ethnicity. In conclusion, differential  VDR  expression relates to ethnicity, rather than 25(OH)D 3  status and  Fok I genotype. Instead, VDR transactivation of  CAMP  is influenced by  Fok I genotype and, together with ethnicity, influence 1,25(OH) 2 D 3 -elicited  CYP24A1  expression. Thus, the expression and role of VDR to transactivate target genes is determined not only by genetics, but also by ethnicity and environment involving complex interactions which may confound disease association.

Vitamin D Receptor Gene Expression and Function in a South African Population: Ethnicity, Vitamin D and FokI